This project focuses on the functional characteristics of molecules that render "fast" synapses, exquisite electrochemical machines, specialized to function on a time scale of milliseconds and a distance scale of micrometers. 1. Functional studies will continue on the nicotinic receptor superfamily. Tethered agonists and cation-it interactions will be studied. Fluorescent probes of receptor conformation will be developed and studied. 2. Structure/function relations will be studied in the P2X receptor superfamily. The mechanism for the large pore that appears after sustained exposure to ATP will be explored. The disulfide topology of the extracellular region will be explored. Mechanisms will be studied for the functional interaction between P2X and nicotinic receptors. 3. The experiments will develop ways to count local densities Of synaptic proteins: transporters, starting with the mouse GABA transporter mGAT1; and receptors, starting with the nAChR alpha4 subunit and P2X2 subunit Ion channels and transporters, including but not limited to those involved in synaptic transmission, are important in many aspects of pathophysiology and therapeutics.